Email Users Custom List new filter

I understand how to create a meta filter for all last names starting with “A” — ‘^A’ — or a range of names “A-C” — ‘^[A-C]’
I have so many subscribers I need to break it down further to keep from breaking the email limits.

What would be the correct code to use if I wanted a list of names “A-Am”?
‘^[A-Am]’ obviously doesn’t work.